1. Field of the Invention
The present invention relates to a metallic double-sided engaging element for a slide fastener, having coupling surfaces on both front and rear surfaces thereof.
2. Description of the Related Art
To open/close an opening in bags or the like, a slide fastener has been known which can be opened in both ways by disposing two sliders such that the sliders collide with their heads or rear ends. In the slide fastener capable of being opened in both ways, double-sided engaging elements whose front and rear coupling surfaces are formed into an equal shape are used to equalize the feeling of operation in both ways for opening backward and opening in the opposite direction. Particularly, a metallic double-sided engaging element excellent in strength, appearance, durability and flexion property is used for clothes and bags employing strong fabric.
For example, Japanese Utility Model Publication No. 55-14252 has disclosed a device for improving a strength resisting a pushing force from the front and rear surfaces and a coupling strength in a rotation direction with respect to an engagement axial line in a slide fastener using metallic double-sided engaging elements.
The double-sided engaging element for the slide fastener described in Japanese Utility Model Publication No. 55-14252 has a central projecting portion in each central portion of a coupling base surface constituting both the front and rear surfaces of a coupling head main body as seen in its plan view, and includes a pair of right and left leg portions, as seen in the plan view, disposed across an engaging element body portion having a larger thickness than the thickness between the coupling base surfaces continuous from the coupling head main body. Right and left projecting portions which project from the body portion toward the coupling head main body side are elevated from the front and rear coupling base surfaces between the central elevated portion and the engaging element body portion. Here, the outer side face of each of right and left projecting portions is flush with right and left side faces of the engaging element body portion. When coupling the double-sided engaging elements with each other, the central elevated portion of a mating element is fit in a dent between the projecting portions while the front end face of the projecting portion is brought into butting a wide front end face at a mating projecting portion front end. Employing the double-sided engaging element having such a shape improves the strength resisting a pushing force against the slide fastener and the coupling strength in the rotation direction with respect to the engagement axial line.
Further, to improve the sealing performance of the slide fastener using the metallic double-sided engaging elements, a slide fastener employing small double-sided engaging elements has been known as disclosed in for example, CN Utility Model Publication No. 2669667Y.
The double-sided engaging element for the slide fastener described in CN Utility Model Publication No. 2669667Y comprises a thin sheet coupling head main body having coupling base surfaces on both front and rear surfaces thereof as seen in a plan view, a thick body portion extending in one direction from the coupling base surface across a stepped surface, and a pair of leg portions extending from the body portion in a direction opposite to the coupling head main body as seen in a plan view. A central elevated portion is elevated from the central portion of the coupling base surface, and a pair of right and left projecting portions project from the body portion to right and left side faces of the central elevated portion. The pair of central elevated portions of a mating double-sided engaging element are detachably coupled in a dent surrounded by the central elevated portion, the right and left projecting portions and the stepped surface between the upper and lower projecting portions.
In the double-sided engaging element for the slide fastener described in CN Utility Model Publication No. 2669667Y, different from the double-sided engaging element described in Japanese Utility Model Publication No. 55-14252, the outer side face of the right and left projecting portions is formed inside of the upper and lower side faces of the engaging element body portion, so that when the double-sided engaging elements are coupled with each other, they can be bent forward or backward easily.
In the meantime, as for the front and rear surfaces mentioned in this specification, if the surface of one side of the coupling surface of the double-sided engaging element is regarded as the front surface, the surface on the opposite side is called a rear surface. As for the front and rear sides, when the closing side when the double-sided engaging element is opened or closed is regarded as the front side, the releasing side on the opposite side is called a rear side, in order to indicate the direction in which the slider is slid. Further, the right and left sides are both sides with respect to the back and forth direction when the central elevated portion is seen in plan view, and the lateral pulling force refers to a direction of separating the double-sided engaging elements in the coupled state.
In the double-sided engaging element for the slide fastener described in Japanese Utility Model Publication No. 55-14252, a dimension between inside elevation startup edges of the right and left projecting portions at a coupling portion is set substantially equal to a dimension between right and left elevation startup edges of the central elevated portion. The right and left projecting portions and the central elevated portion are inclined in a mountainous shape. With this configuration, when the double-sided engaging elements are coupled with each other, a shift between the double-sided engaging elements in the lateral pulling direction and the right and left direction sometimes might be intensified.
When the double-sided engaging elements are coupled with each other, the wide front end faces at the front end of each of the right and left projecting portions in a coupled state are proximate. As a result, as compared to such a large shift in the right and left direction between the double-sided engaging elements as described above, there is a room for improvement in the flexibility of bending the double-sided engaging elements in engagement in a direction that they overlap each other around a coupling axis line when a pushing force is applied to the slide fastener or the flexibility of twisting the elements with respect to the coupling axis line.
On the other hand, also in the double-sided engaging element of the slide fastener described in CN Utility Model Publication No. 2669667Y, when the double-sided engaging elements are coupled with each other, the front ends of right and left projecting portions parallel to each other become proximate. Thus, the flexibility of bending the double-sided engaging elements in engagement in the direction that they overlap around the coupling axis line when the pushing force is applied to the slide fastener is poor. Further, the flexibility of twisting with respect to the coupling axis line is also poor.